GCSEs will be replaced by a system of new I-levels with numbered grades from 1 to 8 under sweeping changes to school exams, according to reports.

England's exam regulator Ofqual is said to be proposing that coursework is axed for all core exams except science, when it would make up just 10% of marks.

The ability to retake the new qualifications would also be limited, with all end-of-course exams sat in the summer apart from English and maths exams in November.

Pupils would therefore have to wait a full year, until they were 17, if they wanted to re-sit any modules - potentially affecting their A-level studies.

A new grade 8 would replace A* as the highest achievement, although fewer would be awarded to help drive up standards, according to The Times.

Education Secretary Michael Gove wants to make exams harder and provide greater differentiation between the most able pupils.

Having 8 rather than 1 at the top would also leave open the option of introducing a grade 9 if it was felt necessary to make it even more challenging.

Schoolchildren currently achieving A* and A grades would apparently be expected to receive grades 7 or 6 under the new system, with grade 4 the equivalent of a pass.

Michael Gove is driving through radical reforms

The changes, which cover English, maths, physics, chemistry, biology, double science, history and geography, would be introduced from 2015.

Other subjects will start to switch from 2016, meaning that during the crossover pupils will sit a mixture of the old and new style of exams.

The plans represent a huge shift in attitude towards coursework, which can currently account for up to 60% of marks at GCSE.

Critics argue this makes it much easier for pupils to achieve high marks - and that it also impinges on valuable teaching time.

However, unions condemned the planned drastic reduction in coursework as illogical and insisting the voices of teachers themselves are listened to.

Christine Blower, general secretary of the National Union of Teachers, said: "The proposals to get rid of coursework from every core subject apart from science are really not the best way forward.

"This will ignore different learning styles and will narrow the skills that can be tested through terminal examinations ...

"This is not what happens at university, so there appears to be no logical reason why it should be so at GCSE or at A-Level. Real life is not about what you can do in two or three hours at the end of a two year process."

The changes are being billed as the most radical overhaul of qualifications since GCSEs were introduced in 1986, replacing the two-tier system of O-levels and CSEs.

Ofqual is said to have decided a new name was needed because the Welsh Assembly is keeping the name GCSE for its exams, which will still include modules and coursework.

Scottish schoolchildren currently study Standard Grades at 15 and 16 and are awarded grades from 1 to 7.

The watchdog for England has apparently rejected some of Mr Gove's proposals, such as limiting the number of candidates given each grade and stating their strengths and weaknesses.

A spokesman for the watchdog refused to discuss the details but the body is due to launch a consultation on the changes shortly.

Mr Gove had called for the axing of GCSEs in favour of an English Baccalaureate Certificate but later admitted this reform was a "bridge too far".

Shadow education secretary Stephen Twigg: "This is now the third time Michael Gove has tried to abolish GCSEs. He keeps failing because he hasn't got a thought through plan to improve exams.

"Changing letters to numbers and the name of the exams is hardly the key to higher standards. We need serious proposals that learn from the best countries in the world.

"This needs a rigorous focus on English and maths and testing both academic knowledge and the skills that young people will need in the workplace."